1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device capable of improving aperture ratio by reducing the size of black matrix on a predetermined part or removing the black matrix using a wide view angle method.
2. Description of the Related Art
As well known, a conventional liquid crystal display device has generally employed a twisted nematic (TN) mode, which has a disadvantage of narrow view angle. In order to solve the problem, a fringe field switching (FFS) mode liquid crystal display device has been proposed.
However, according to the conventional structures, although off voltage corresponding to 0V is applied to a pixel electrode and a counter electrode, a predetermined signal is continuously applied to data bus lines to turn on other pixels. Therefore, a noise field is formed between the data bus line and the pixel electrode or between the data bus line and the counter electrode. As a result, liquid crystal molecules are separated from a polarizer axis and light is leaked through the portion. Then, a large black matrix (BM) patterning is required on the upper substrate to prevent the leakage light, thereby reducing aperture ratio in a panel.
Moreover, the black matrix is formed in consideration of assembly margin of upper and lower substrates. Therefore, the reduced aperture ratio makes it difficult to realize high brightness.
FIG. 1A shows a pixel structure of conventional FFS mode. FIG. 1B shows a liquid crystal molecule forming a predetermined angle with the noise field and FIG. 1C relation of the liquid crystal molecule and a polarizing plate.
Referring to the FIGS. 1A-1C, in order to obtain maximum transmittance, negative liquid crystals are rubbed by .+xe2x88x92.12.degree. to a gate bus line 2 and positive liquid crystals by .+xe2x88x92.78.degree. to the gate bus line. Therefore, early liquid crystal molecules 3 are controlled to correspond with the rubbing direction A (as shown in FIG. 1B).
Here; a Noise Field 10 (as shown in FIGS. 1A-1B) is formed between a data bus line 4 and a pixel electrode 6 or between the data bus line 4 and a counter electrode 8.
FIG. 1B is a drawing for showing the operation of liquid crystal molecules 3 to the noise field 10, the liquid crystal molecules forming a predetermined angle with the noise field 10, wherein negative liquid crystals are arranged, the major axis of the liquid crystal molecule 3 being perpendicular to the noise field 10 and positive liquid crystals are arranged, the major axis of the liquid crystal molecule 3 being parallel to the noise field. As a result, as shown in FIG. 1C, the liquid crystal molecules 3 are separated by a predetermined angle from the polarizer axis of the polarizing plate, thereby generating leakage light around the data line 4 at off state.
FIG. 2 is a cross sectional view of conventional liquid crystal display device. As described above, the liquid crystal molecules 3 are separated from the polarizer axis of the polarizing plate 12 by the noise field 10 between the data bus line 4 and the pixel electrode 6 or between the data bus line 4 and the counter electrode 8. Therefore, a large black matrix layer 22, having a width of approximately 27 xcexcm, is formed on the data bus line 4 in order to prevent leakage light around the data bus line 4.
And, on the gate bus line 2, the black matrix region 22 is formed to have a width of approximately 500 xcexcm. Therefore, aperture ratio is reduced, thereby lowering brightness of panel.
A conventional in-plane switching (IPS) mode also has the above-mentioned problems.
It is therefore an object of the present invention to provide a liquid crystal display device capable of realizing high aperture ratio and high brightness by reducing or removing a conventional black matrix layer.
To achieve the above and other objects, the present invention provides a liquid crystal display device that comprises a lower substrate and an upper substrate confronting each other; a counter electrode formed on the lower substrate; a pixel electrode formed on the counter electrode with an insulating layer interposed; a lower polarizing plate and an upper polarizing plate attached on respective outer sides of the lower and the upper substrates; a gate bus line; and a data bus line.
Particularly, in the device of the invention, a rubbing direction of the lower substrate corresponds with a direction of noise field formed between the data bus line and the pixel electrode or the counter electrode and between the gate bus line and the pixel electrode or the counter electrode.
Preferably, the counter electrode may have a shape of box (i.e. generally a planar, rectangular shape) made of a first ITO and the pixel electrode may be formed by patterning a second ITO to have a shape of clamp (i.e., a clamp having two legs with one end of each leg pinned together for pivoting so as to resemble generally a xe2x80x9cVxe2x80x9d shape) in one sub-pixel or to alternatively have a slant line (/) shape and an inverse-slant line ( ) shape by sub-pixels (i.e. each generally V shaped pixel electrode being in a sub-pixel), thereby having FFS mode.
Furthermore, the counter electrode and the pixel electrode may be made of opaque metal and respectively patterned to have a shape of clamp in one sub-pixel or to alternatively have a slant line (/) shape and an inverse-slant line ( ) shape by sub-pixels, thereby having IPS mode.
Furthermore, when the rubbing direction of the lower substrate is parallel to the gate bus line, the noise field may be formed between the data bus line and the counter electrode or between the data bus line and the pixel electrode and therefore, a black matrix of the upper substrate may be narrowly formed on the data bus line, or ther is no black matrix of the upper substrate.
Preferably, the black matrix of the upper substrate has a width the same as or smaller than the distance between the counter electrodes formed with the data bus line interposed and more preferably, less than 6 xcexcm.
And, when the rubbing direction of the lower substrate is perpendicular to the gate bus line, the noise field is formed between the gate bus line and the counter electrode or between the gate bus line and the pixel electrode and therefore, black matrix of the upper substrate is formed on the gate bus line, to have a width the same as or smaller than that of the gate bus line.
Furthermore, the rubbing direction of the lower substrate may be perpendicular to the gate bus line and there may be no black of the upper substrate.
Preferably, the upper substrate may have a rubbing direction anti-parallel or parallel to that of the lower substrate. In addition, the lower polarizing plate may have a polarizer axis corresponding with the rubbing direction of the lower substrate, and the upper polarizing plate may have an analyzer axis perpendicular to the rubbing direction of the lower substrate.